Corrugated compression type electric cables



A; N. ARMAN 2,866,843

CORRUGATED COMPRESSION TYPE ELECTRIC CABLES Dec. 30, 1953 Filed Aug. 25, 1954 FIG 1,.

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\NVENTOR "BY W faxa m0 EY United States Patent Of CORRUGATED COMPRESSION TYPE ELECTRIC CABLES Adrian Neville Arman, London, England, assignor to Pirelli-General Cable Works Limited, London, England, a British company Application August 23, 1954, Serial No. 451,435 1 Claim. Cl. 174-25 The present invention relates to electric cables and is particularly concerned with that type known as compression cables. In such a cable the cable core or cores, impregnated with a viscous compound, is or are contained within a comparatively thin flexible sheath which is surrounded by a second sheath capable of withstanding substantial internal fluid pressure, there being one or more spaces between the sheaths filled with fluid, normally gas, at a pressure which may amount to 200 pounds per square inch or even higher. The inner sheath may be of circular cross section, but it has been common practice to make it otherwise. For instance, in the case of a single-core cable, the sheath may be of oval section, the core being either circular or oval, or in a threecore cable the inner sheath has been made triangular with rounded corners to conform to the contour of the cores. The effect of this is to allow the pressure fluid to compress the dielectric within the inner sheath and, in cases in which it is of non-circular cross section, the sheath acts as a flexible diaphragm to accommodate expansion and contraction of the dielectric compound with temperature variation.

Hitherto it has been common practice to make the inner sheath of lead, but it is well known that, if it is to act efficiently as a flexible diaphragm in the manner above stated, it is advantageous that it shall be made of a metal possessing substantially greater elasticity than that of lead, such, for instance, as aluminium. In that case, however, in order that the sheath shall respond readily to temperature variations of the viscous compound, it is desirable that it shall be very thin, with the result that it becomes liable to buckle on bending the cable. The present invention has for its main object to overcome this disadvantage.

According to the invention, in a compression cable the inner sheath is made of metal, such as aluminium, possessing substantial elasticity as compared with lead, and the outer sheath, of a like metal, is corrugated circumferentially, the corrugations being of such a depth as to make firm contact at two or more points with the inner sheath. Thus the outer sheath serves to support the inner sheath and to impart to the latter a degree of resistance to buckling, although the outer sheath itself is capable of being bent to a reasonable extent without buckling by reason of its circumferential corrugations. The latter may lie strictly at right angles to the axis of the sheath or may be helical in form. The inner sheath is non-circular in order to afford the breathing action above referred to.

In order that the invention may be clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing, which illustrates by way of example, two forms of cable in accordance therewith and wherein:

Figure l is a longitudinal elevation wherein the constituent elements are successively cut back andFigure 2 is a cross section of a single-core cable, and

2,866,843 Patented Dec. 30, 1958 ice three-core cable.

Referring to Figures 1 and 2, the conductor-1, which would normally be constituted by a series of stranded wires, is surrounded by suitable insulation 2, the core thus formed being enclosed in an inner sheath 3 of oval cross section and of a metal possessing elasticity substantially greater than that of lead, such for instance, as aluminium. The sheath 3 is filled with a viscous compound whereby the insulation 2 of the cable core is impregnated. Surrounding the sheath 3 there is an external sheath 4, also of a metal possessing elasticity substantially greater than that of lead, of circular cross section and circumferentially corrugated, the corrugations being in this instance helical in form as indicated. The diameter of the sheath and the depth of the corrugations are such that the latter make firm contact with the inner sheath 3 at two points on its major axis, as shown in Figure 2. Thus, on each side of the sheath 3, there is a space 5 which is filled with gas or other fluid at a relatively high pressure, for example, 200 pounds per square inch. By reason of the fact that the sheath 4 is corrugated, however, these two spaces are necessarily in communication.

In the case of the three-core cable depicted in Figures 3 and 4, the cable cores are arranged in triangular relationship and the inner sheath 3 is of overall triangular cross section having its corners rounded to conform to each cable core. In this case the dimensions of the outer sheath 4 are such that the corrugations bear on the inner sheath 3 at the rounded corners of the latter, as clearly seen in Figure 4. This results in the production of three inter-communicating spaces 5 which are filled with gas or other fluid at high pressure.

The sheaths may be of any metal possessing the requisite elasticity as above set forth, for instance, alumin ium, aluminium alloy, stainless steel or copper. Also it is not necessary that both sheaths should be of the same metal.

It is to be understood that, in cables according to the present invention, the metal of the sheaths employed is continuous in the longitudinal direction, as distinct from sheaths formed, for instance, by helically winding a strip whereof the convolutions interlock. Either of the sheaths used according to the present invention may be formed by helically winding a metal strip, but in such a case, the edges of adjacent convolutions would be joined by a welding, soldering or like process ensuring complete continuity of the metal in the longitudinal direction and therefore fluid-tightness of the sheath. In the appended claim the word continuous is to be understood as hearing the above meaning.

What I claim and desire to secure by Letters Patent in the United States is:

A compression type electric cable comprising in combination at least one cable core, a fluid-tight continuous cable core-receiving inner sheath of non-circular and substantially uniform cross section and made of metal possessing substantial elasticity as compared with lead, a core-impregnating fluid in said inner sheath, means for counteracting the formation of outward folds or wrinkles in said inner sheath on bending it in the axial direction, said means comprising a fluid-tight continuous outer sheath surrounding said inner sheath and formed of like metal, said outer sheath being corrugated circumferentially and said outer sheath corrugations being of such a depth as to make firm contact with the inner sheath at at least two points on the periphery of each complete circumferential corrugation.

(References on following page) Referencescitedin file of this-patent UNITED STATES PATENTS Hunter Sept. 4, 1934 Vbge1 Sent. 1936 5 Fredrickson Jan, 12,.. 1943 Johnstone Men; 18,,1952

4 FOREIGN PATENTS Switzerland Oct. 17, 1938 Great Britain Oct. 11, 1939 Great Britain May 23, 1949 Great Britain Aug. 22, 1951 Great Brit a in Mar. 18, 1953 

